Are learning disabilities found in children with parents that were cousins an what neurological disease can be caused by this. Also.?

Genetic. Learning disabilities are genetic disorders and run in families but not necessarily in intermarried cousins. It is true that consanguinity tends to cause more genetic disorders.
See below. Consanguinity or close relations between immediately related kin (cousins, brothers, sister, parents, uncles, aunts) producing children can result in a variety of genetic problems due combining similar genes with similar mutations or traits that alone are not problem forming but when combined together cause many genetic defects. Thus the reason for the ancient beliefs against incest.